EspC (Escherichia coli secreted protein C) of enteropathogenic E. coli (EPEC) shows the three classical domains of the autotransporter proteins and has a conserved serine protease motif belonging to the SPATE (serine protease autotransporters of Enterobacteriaceae) subfamily. EspC and its homolog Pet in enteroaggregative E. coli (EAEC) bear the same sequence within the serine protease motif, and both proteins produce enterotoxic effects, suggesting that like Pet, EspC could be internalized to reach and cleave the calmodulinbinding domain of fodrin, causing actin cytoskeleton disruption. Even though both proteins cause cytoskeleton damage by virtue of their serine protease motifs, the following evidence supports the hypothesis that the mechanisms are different. All these data suggest that the protein conformational structure is very important for the activity of the catalytic site, influencing its interaction with the target protein and its internalization. The differences between these proteins may explain the reduced ability of EspC to cause cytopathic effects. However, these differences may confer a specialized role on EspC in the pathogenesis of EPEC, which is different from that of Pet in EAEC pathogenesis.Enteropathogenic Escherichia coli (EPEC), a leading cause of infantile diarrhea in developing countries, secretes effector molecules which allow bacteria to interact with their hosts and cause disease (7,11). EPEC secretes at least six proteins (Esp [E. coli secreted proteins]), four of which, EspA (11), EspD (14), EspB (26), and EspF (16), are secreted by a type III secretion system. Esp molecules as well as the secretion apparatus are encoded within a 35.6-kb pathogenicity island termed the locus of enterocyte effacement (LEE) (4, 15). EspA, EspD, and EspB proteins form a translocon for delivering effector molecules into the host cytosol (12,22). Tir (translocated intimin receptor) is translocated through this apparatus (10) and serves as a receptor for the EPEC adhesin intimin (9). Intimin is required for intimate bacterial attachment to host cells (8) and to focus the polymerization of cytoskeletal rearrangements leading to the disruption of intestinal microvilli, a phenotype known as the attaching and effacing (A/E) lesion (18).In addition to the secretion of the proteins via the type III secretion system mentioned above, EPEC also secretes a protein via the type V secretion system, the autotransporter pathway (25). This protein, EspC, shows the three classical domains (signal peptide, passenger domain, and ␤-domain) of the autotransporter proteins, which were first described for the immunoglobulin A (IgA) protease of Neisseria gonorrhoeae (23,25). EspC also has a conserved serine protease motif similar to the IgA protease but does not cleave IgA, as do several other members of the autotransporter family of proteins. In fact, EspC belongs to the subfamily of serine protease autotransporters of Enterobacteriaceae (SPATE) including Tsh, SepA, Pic, EspP, Sat, and Pet; none of these cleave IgA. Moreover, ...

Sperm motility is a must for natural fertilization to occur. During their travel through the epididymis, mammalian spermatozoa gradually acquire the ability to move. This is accomplished through a sliding movement of the outer doublet microtubules of the axoneme which is energized by the dynein ATPase. Within its complex structure, the mammalian sperm flagellum contains F-actin and thus, we decided to test in the guinea pig sperm flagellum the role of F-actin in motility. During maturation, capacitation, and the acrosome reaction, a gradual decrease of the relative concentration of F-actin was observed. Motility increased as spermatozoa became able to fertilize. Gelsolin, phalloidin, and KI inhibited sperm motility. Gelsolin canceled sperm motility within 20 min of treatment while 0.6 M KI had immediate effects. Phalloidin diminished hyperactive sperm motility slightly. All three compounds significantly increased the relative concentration of F-actin. Latrunculins are conventional drugs that destabilize the F-actin cytoskeleton. Latrunculin A (LAT A) did not affect sperm motility; but significantly increased F-actin relative concentration. The results suggested that in guinea pig spermatozoa, randomly severing F-actin filaments inhibits flagellar motility; while end filament alteration does not. Thus, specific filament regions seem to be important for sperm motility.